1. Field of the Invention
The invention relates to electronically.-controlled phase shifting of microwave signals. This technology is widely used for steering microwave beams in scanning antenna radar systems.
2. Description of the Prior Art
An inexpensive, easily manufacturable alternative to ferrite phase shifters is needed for steering microwave radar beams. Phase shifting in radars is normally accomplished using magnetic ferrite-dielectric composites which must be manually assembled. This assembly greatly increases the cost of these components. Additionally, ferrite-dielectric composite phase shifters are relatively heavy, large, and are susceptible to shock. An improvement to a magnetic ferrite-dielectric composite phase shifter is a ceramic phase shifter. U.S. Pat. No. 5,032,805, granted to Elmer et al. disclosed a voltage-controlled ceramic phase shifter. This patent employed strontium-barium titanate as the active material. Ceramics, however, are not an accepted microwave media. Additionally, they require embedding in compounds which makes assembly difficult, and require the careful selection of filler compounds with low microwave losses and matching coefficients of expansion. U.S. Pat. No. 5,032,805 did discuss a stripline application of the Elmer phase shifter, but relied on impedance matching wedges rather than the preferable .lambda./4 wave transformer impedance matching technique disclosed in the present invention. Additionally, the DC blocking function in U.S. Pat. No. 5,032,805 is accomplished with a capacitor, which being exposed to air, is subject to arcing. The present invention relies instead on a DC blocking circuit in its ground plane which is enclosed in silicone to allow the use of higher voltages.